| CHMOD(1) |
AerieBSD 1.0 Refernce Manual |
CHMOD(1) |
NAME
chmod —
change file modes
SYNOPSIS
chmod
.Oo
-R
[-H | L | P]
.Oc
mode
DESCRIPTION
The
chmod
utility modifies the file mode bits of the listed files
as specified by the
mode
operand.
The mode of a file dictates its permissions, among other attributes.
The options are as follows:
- -H
-
If the
-R
option is also specified, symbolic links on the command line are followed.
(Symbolic links encountered in the tree traversal are not followed.)
- -L
-
If the
-R
option is also specified, all symbolic links are followed.
- -P
-
If the
-R
option is also specified, no symbolic links are followed.
- -R
-
Recursively descend through any specified directory arguments.
Change the modes of the file hierarchies rooted in the files
instead of just the files themselves.
Symbolic links do not have modes, so unless the
-H
or
-L
option is set,
chmod
on a symbolic link always succeeds and has no effect.
The
-H,
-L,
and
-P
options are ignored unless the
-R
option is specified.
In addition, these options override each other and the
command's actions are determined by the last one specified.
Only the file's owner or the superuser is permitted to change
the mode of a file.
The
chmod
utility exits 0 on success or >0 if an error occurred.
Absolute modes
Absolute modes are specified according to the following format:
chmod
nnnn
file
[]...
An absolute mode is an octal number (specified as
nnnn,
where
n
is a number from 0 to 7) constructed by ORing
any of the following values:
- 0400
-
Allow read by owner.
- 0200
-
Allow write by owner.
- 0100
-
Allow execution (or search in directories) by owner.
- 0700
-
Allow read, write, and execute/search by owner.
- 0040
-
Allow read by group.
- 0020
-
Allow write by group.
- 0010
-
Allow execution (or search in directories) by group.
- 0070
-
Allow read, write, and execute/search by group.
- 0004
-
Allow read by others.
- 0002
-
Allow write by others.
- 0001
-
Allow execution (or search in directories) by others.
- 0007
-
Allow read, write, and execute/search by others.
In addition to the file permission modes, the following mode bits are
available:
- 4000
-
Set-user-ID on execution.
- 2000
-
Set-group-ID on execution.
- 1000
-
Enable sticky bit; see
sticky(8)
and
chmod(2).
The execute bit for a directory is often referred to as the
“search”
bit.
In order to access a file, a user must have execute permission in each
directory leading up to it in the filesystem hierarchy.
For example, to access the file
/bin/ls,
execute permission is needed on
/,
/bin,
and, of course, the
ls
binary itself.
Symbolic modes
Symbolic modes are specified according to the following format:
chmod
.Sm off
‹
[who]
op
[perm]
›
[who]
op
[perm]
.Oc Ns Li , Op Ar ...
.Sm on
file
[]...
The
who
symbols indicate whose permissions are to be changed or assigned:
- u
-
User (owner) permissions.
- g
-
Group permissions.
- o
-
Others permissions.
- a
-
All of the above.
Do not confuse the
‘o’
symbol with
“owner”.
It is the user bit,
‘u’,
that refers to the owner of the file.
The
op
symbols represent the operation performed, as follows:
- +
-
If no value is supplied for
perm,
the
‘+’
operation has no effect.
If no value is supplied for
who,
each permission bit specified in
perm,
for which the corresponding bit in the file mode creation mask
is clear, is set.
Otherwise, the mode bits represented by the specified
who
and
perm
values are set.
- \&\-
-
If no value is supplied for
perm,
the
‘\-’
operation has no effect.
If no value is supplied for
who,
each permission bit specified in
perm,
for which the corresponding bit in the file mode creation mask
is clear, is cleared.
Otherwise, the mode bits represented by the specified
who
and
perm
values are cleared.
- =
-
The mode bits specified by the
who
value are cleared, or, if no
who
value is specified, the user, group
and other mode bits are cleared.
Then, if no value is supplied for
who,
each permission bit specified in
perm,
for which the corresponding bit in the file mode creation mask
is clear, is set.
Otherwise, the mode bits represented by the specified
who
and
perm
values are set.
The
perm
(permission symbols) represent the portions of the mode bits as follows:
- r
-
Read bits.
- s
-
Set-user-ID and set-group-ID on execution bits.
- t
-
Sticky bit.
- w
-
Write bits.
- x
-
Execute/search bits.
- X
-
The execute/search bits if the file is a directory or any of the
execute/search bits are set in the original (unmodified) mode.
Operations with the
perm
symbol
‘X’
are only meaningful in conjunction with the
op
symbol
‘+’,
and are ignored in all other cases.
- u
-
User permission bits in the mode of the original file.
- g
-
Group permission bits in the mode of the original file.
- o
-
Other permission bits in the mode of the original file.
Each clause (given in a comma-delimited list on the command line) specifies
one or more operations to be performed on the mode bits, and each operation is
applied in the order specified.
Operations upon the
“other”
permissions (specified by the symbol
‘o’
by itself), in combination with the
perm
symbols
‘s’
or
‘t’,
are ignored.
EXAMPLES
Set file readable by anyone and writable by the owner only:
$ chmod 644 file
Deny write permission to group and others:
$ chmod go-w file
Set the read and write permissions to the usual defaults, but
retain any execute permissions that are currently set:
$ chmod =rw,+X file
Make a directory or file searchable/executable by everyone if it is
already searchable/executable by anyone:
$ chmod +X file
Any of these commands will make a file readable/executable by everyone and
writable by the owner only:
$ chmod 755 file
$ chmod u=rwx,go=rx file
$ chmod u=rwx,go=u-w file
Clear all mode bits for group and others:
$ chmod go= file
Set the group bits equal to the user bits, but clear the group write bit:
$ chmod g=u-w file
SEE ALSO
chflags(1),
chgrp(1),
find(1),
install(1),
chmod(2),
stat(2),
umask(2),
fts(3),
setmode(3),
symlink(7),
chown(8),
sticky(8)
STANDARDS
The
chmod
utility is compliant with the
specification.
The flags
[-HLP]
are extensions to that specification.
HISTORY
A
chmod
command appeared in
Version 1 AT&T UNIX.
BUGS
There's no
perm
option for the naughty bits.
| AerieBSD 1.0 Reference Manual |
August 26 2008 |
CHMOD(1) |